More Moon and Jupiter

There’s a beautiful conjunction in the sky tonight — a pairing of the Moon and Jupiter. The brilliant planet is to the right of the Moon at nightfall, and below the Moon as they set in the wee hours of the morning.

If you could float atop Jupiter’s atmosphere, you’d see four large moons crossing the night sky, not just one.

The most prominent would be Io. It’s the closest of the four — a little closer than our moon is to Earth. It’s also a little bit larger than our moon is, and it’s much more reflective.

This big, bright moon would put on quite a show. Io is the most volcanically active body in the solar system. The volcanoes have painted its surface in shades of yellow, white, and red. And they frequently produce giant plumes large enough to see from Jupiter. Some of them would rise above Io’s edge like little umbrellas.

You wouldn’t see a full Io, though, because the moon always passes through Jupiter’s shadow, creating an eclipse. Yet Io wouldn’t disappear from view. Some of its volcanoes are so hot that they’d be bright enough to see even when the moon is eclipsed.

One other impressive feature about Io would be its speed across the sky. In a single Jovian night, which lasts about five hours, Io would race about 40 degrees across the background of stars — four times the width of your fist held at arm’s length. In that same amount of time, our moon moves just three degrees — which is why it can hang out close to Jupiter all night.

Script by Damond Benningfield, Copyright 2011

For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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